Gas turbine engine variable area fan nozzle control

ABSTRACT

A method of managing a gas turbine engine includes the steps of detecting an airspeed and detecting a fan speed. A parameter relationship is referenced related to a desired variable area fan nozzle position based upon at least airspeed and fan speed. The detected airspeed and detected fan speed is compared to the parameter relationship to determine a target variable area fan nozzle position. An actual variable area fan nozzle position is adjusted in response to the determination of the target area fan nozzle position and at least one threshold.

This application is a continuation of U.S. Ser. No. 13/365,455, whichwas filed on Feb. 03, 2012 which claims priority to U.S. ProvisionalApplication No. 61/592,984, which was filed on Jan. 31, 2012.

BACKGROUND

This disclosure relates to managing gas turbine engine fan operabilityand operating characteristics using a variable area fan nozzle.

One typical gas turbine engine includes low and high speed spools housedwithin a core nacelle. The low speed spool supports a low pressurecompressor and turbine, and the high speed spool supports a highpressure compressor and turbine. A fan is coupled to the low speedspool. A fan nacelle surrounds the fan and core nacelle to provide abypass flow path having a nozzle. Typically, the nozzle is a fixedstructure providing a fixed nozzle exit area.

The fan's operating line must be controlled to avoid undesiredconditions such as fan flutter, surge or stall. The fan operating linecan be manipulated during engine operation to ensure that the fanoperability margin is sufficient. The fan operating line is defined, forexample, by characteristics including low spool speed, bypass airflowand turbofan pressure ratio. Manipulating any one of thesecharacteristics can change the fan operating line to meet the desiredfan operability margin to avoid undesired conditions.

The engine is designed to meet the fan operability line and optimize theoverall engine performance throughout the flight envelope. As a result,the engine design is compromised to accommodate various engine operatingconditions that may occur during the flight envelope. For example, fuelconsumption for some engine operating conditions may be less thandesired in order to maintain the fan operating line with an adequatemargin for all engine operating conditions. For example, fan operatingcharacteristics are compromised, to varying degrees, from high Machnumber flight conditions to ground idle conditions for fixed nozzle areaturbofan engines. This creates design challenges and/or performancepenalties to manage the operability requirements.

SUMMARY

In one exemplary embodiment, a method of managing a gas turbine engineincludes the steps of detecting an airspeed and detecting a fan speed. Aparameter relationship is referenced related to a desired variable areafan nozzle position based upon at least airspeed and fan speed. Thedetected airspeed and detected fan speed is compared to the parameterrelationship to determine a target variable area fan nozzle position. Anactual variable area fan nozzle position is adjusted in response to thedetermination of the target area fan nozzle position and at least onethreshold.

In a further embodiment of any of the above, the fan speed detectingstep includes detecting a low speed spool rotational speed andcorrecting the fan speed based upon an ambient temperature.

In a further embodiment of any of the above, the fan speed detectingstep includes calculating the fan speed based upon a gear reductionratio.

In a further embodiment of any of the above, the referencing andcomparing steps include providing a target variable area fan nozzleposition for a range of air speeds based upon the fan speed.

In a further embodiment of any of the above, the air speed range is0.35-0.55 Mach. The data table includes first and second thresholdscorresponding to lower and upper fan speed limits. The target variablearea fan nozzle position is selected based upon the first and secondthresholds.

In a further embodiment of any of the above, the upper fan speed limitis 60% of an aerodynamic design speed of the fan, and the lower fanspeed limit is 75% of the aerodynamic design speed of the fan.

In a further embodiment of any of the above, the upper fan speed limitis 65% of the aerodynamic design speed of the fan.

In a further embodiment of any of the above, the lower fan speed limitis 75% of the aerodynamic design speed of the fan.

In a further embodiment of any of the above, the adjusting step includesadjusting the target variable fan nozzle position to provide an exitarea of a fan nacelle.

In a further embodiment of any of the above, the adjusting step includestranslating the flaps to selectively block a vent in the fan nacelle.

In a further embodiment of any of the above, the gas turbine engineincludes a fan arranged in a fan nacelle having a flap configured to bemovable between first and second positions. An actuator is operativelycoupled to the flap. A compressor section is fluidly connected to thefan, and the compressor includes a high pressure compressor and a lowpressure compressor. A combustor is fluidly connected to the compressorsection, and a turbine section is fluidly connected to the combustor.The turbine section includes a high pressure turbine coupled to the highpressure compressor via a shaft, and a low pressure turbine.

In a further embodiment of any of the above, the gas turbine engine is ageared aircraft engine having a bypass ratio of greater than about six(6).

In a further embodiment of any of the above, the gas turbine engineincludes a low Fan Pressure Ratio of less than about 1.45.

In a further embodiment of any of the above, the low pressure turbinehas a pressure ratio that is greater than about 5.

In another exemplary embodiment, a gas turbine engine includes a fannacelle that includes a flap that is configured to be movable betweenfirst and second positions. An actuator is operatively coupled to theflap. A controller is configured to reference a parameter relationshipthat relates to a desired variable area fan nozzle position based uponat least airspeed and fan speed. The controller is configured to comparea detected airspeed and a detected fan speed to the parameterrelationship to determine a target variable area fan nozzle position.The controller is configured to provide a command to the actuator toadjust the flap from a first position to the second position in responseto the determination of the target variable fan nozzle position and atleast one threshold.

In a further embodiment of any of the above, a fan is arranged in thefan nacelle. A compressor section is fluidly connected to the fan, andthe compressor includes a high pressure compressor and a low pressurecompressor. A combustor is fluidly connected to the compressor section,and a turbine section is fluidly connected to the combustor. The turbinesection includes a high pressure turbine coupled to the high pressurecompressor via a shaft, and a low pressure turbine.

In a further embodiment of any of the above, the gas turbine engine is ageared aircraft engine having a bypass ratio of greater than about six(6).

In a further embodiment of any of the above, the gas turbine engineincludes a low Fan Pressure Ratio of less than about 1.45.

In a further embodiment of any of the above, the low pressure turbinehas a pressure ratio that is greater than about 5.

In a further embodiment of any of the above, the controller isconfigured to provide a target variable area fan nozzle position for arange of air speeds based upon the fan speed. The air speed range is0.35-0.55 Mach. The data table includes first and second thresholds thatcorrespond to lower and upper fan speed limits. The target variable areafan nozzle position is selected based upon the first and secondthresholds.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be further understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 schematically illustrates an example gas turbine engine.

FIG. 2 is an example schedule for varying a fan nacelle exit area basedupon air speed and fan speed.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. Alternative engines mightinclude an augmentor section (not shown) among other systems orfeatures. The fan section 22 drives air along a bypass flowpath whilethe compressor section 24 drives air along a core flowpath forcompression and communication into the combustor section 26 thenexpansion through the turbine section 28. Although depicted as aturbofan gas turbine engine in the disclosed non-limiting embodiment, itshould be understood that the concepts described herein are not limitedto use with turbofans as the teachings may be applied to other types ofturbine engines including three-spool architectures.

The engine 20 generally includes a low speed spool 30 and a high speedspool 32 mounted for rotation about an engine central longitudinal axisA relative to an engine static structure 36 via several bearing systems38. It should be understood that various bearing systems 38 at variouslocations may alternatively or additionally be provided.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects a fan 42, a low pressure compressor 44 and a low pressureturbine 46. The inner shaft 40 is connected to the fan 42 through ageared architecture 48 to drive the fan 42 at a lower speed than the lowspeed spool 30. The high speed spool 32 includes an outer shaft 50 thatinterconnects a high pressure compressor 52 and high pressure turbine54. A combustor 56 is arranged between the high pressure compressor 52and the high pressure turbine 54. A mid-turbine frame 57 of the enginestatic structure 36 is arranged generally between the high pressureturbine 54 and the low pressure turbine 46. The mid-turbine frame 57supports one or more bearing systems 38 in the turbine section 28. Theinner shaft 40 and the outer shaft 50 are concentric and rotate viabearing systems 38 about the engine central longitudinal axis A, whichis collinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 57 includes airfoils 59 whichare in the core airflow path. The turbines 46, 54 rotationally drive therespective low speed spool 30 and high speed spool 32 in response to theexpansion.

The engine 20 in one example a high-bypass geared aircraft engine. In afurther example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than ten (10), the gearedarchitecture 48 is an epicyclic gear train, such as a planetary gearsystem or other gear system, with a gear reduction ratio of greater thanabout 2.3 and, for example, greater than about 2.5:1 and the lowpressure turbine 46 has a pressure ratio that is greater than about 5.In one disclosed embodiment, the engine 20 bypass ratio is greater thanabout ten (10:1), the fan diameter is significantly larger than that ofthe low pressure compressor 44, and the low pressure turbine 46 has apressure ratio that is greater than about 5:1. Low pressure turbine 46pressure ratio is pressure measured prior to inlet of low pressureturbine 46 as related to the pressure at the outlet of the low pressureturbine 46 prior to an exhaust nozzle. It should be understood, however,that the above parameters are only exemplary of one embodiment of ageared architecture engine and that the present invention is applicableto other gas turbine engines including direct drive turbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, withthe engine at its best fuel consumption—also known as “bucket cruiseThrust Specific Fuel Consumption (‘TSFC’)”—is the industry standardparameter of lbm per hour of fuel being burned divided by lbf of thrustthe engine produces at that minimum point. “Low fan pressure ratio” isthe pressure ratio across the fan blade alone, regardless of thepresence of a Fan Exit Guide Vane (“FEGV”) system. The low fan pressureratio as disclosed herein according to one non-limiting embodiment isless than about 1.45. “Low corrected fan tip speed” is the actual fantip speed in ft/sec divided by an industry standard temperaturecorrection of [(Tambient deg R)/518.7)̂0.5]. The “Low corrected fan tipspeed,” as disclosed herein according to one non-limiting embodiment, isless than about 1150 ft/second.

A core nacelle 61 surrounds the engine static structure 36. A fannacelle 58 surrounds the core nacelle 61 to provide the bypass flowpath. In the example engine 20, a nozzle exit area 60 is effectivelyvariable to alter the bypass flow B and achieve a desired targetoperability line. In one example, the fan nacelle 58 includes moveableflaps 62 near the bypass flowpath exit, which may be provided by arcuatesegments that are generally linearly translatable parallel to the axis Ain response to inputs by one or more actuators 66.

The flaps 62 are moveable between first and second positions P1, P2 andpositions in between. The flaps 62 selectively regulate by blocking, asize of an annular vent 64 provided between a trailing end 63 of thenacelle body and a leading edge 65 of the flaps 62. The vent 64 is fullyopen in the second position P2, in which a vent flow V from the bypassflowpath is permitted to exit through the vent 64. An open vent 64increases the bypass flow B and effectively increases the nozzle exitarea 60. With the flaps 62 in the first position P1, flow from thebypass flowpath is not permitted to pass through the vent 64, which isblocked by the flaps 62.

A controller 68 is in communication with a low speed spool sensor 70,which detects a rotational speed of the low speed spool 30. Atemperature sensor 72 detects the ambient temperature. Air speed 74 isprovided to the controller 68, as is the ambient temperature. In theexample, the controller 68 may store various parameters 76 relating tothe engine 20, such as a gear reduction ratio of the geared architecture48, outer diameter of the fan 22 and other information useful incalculating a low corrected fan tip speed.

A parameter relationship 78, which may be one or more data tables and/orequations and/or input-output data chart etc., for example, may bestored in the controller 68. The parameter relationship 78 includesinformation relating to air speed, fan speed and a desired variable areafan nozzle position, which provide a schedule illustrated in FIG. 2. Oneexample of the parameter relationship 78 is a bivarient lookup table. Inoperation, the turbofan engine operating line is managed by detectingthe air speed and the fan speed, for example, by determining the lowspeed spool rotational speed. In should be understood, however, that thefan speed may be inferred from the low speed spool rotational speedrather than calculated. That is, only the low speed spool rotationalspeed could be monitored and compared to a reference low speed spoolrotational speed in the parameter relationship 78, rather than a fanspeed. The controller 68 references the parameter relationship 78, whichincludes a desired variable area fan nozzle position relative to the airspeed and fan speed. The detected air speed and fan speed, which may bedetected in any order, are compared to the data table to provide atarget variable area fan nozzle position. The controller 68 commands theactuators 66 to adjust the flaps 62 from an actual variable area fannozzle position, or the current flap position, to the target variablearea fan nozzle position.

One example schedule is illustrated in FIG. 2. Multiple data curves areprovided, which correspond to different fan speeds. The curves, whichare linear in one example, provide first and second thresholds 80, 82that respectively relate to upper and lower limits for the targetvariable area fan nozzle position as it relates to a range of airspeeds. As shown in the example in FIG. 2, air speeds of between about0.35 Mach and 0.55 Mach, and in one example, between about 0.38 Mach and0.50 Mach, provide a region in which the nozzle exit area is adjustedbased upon fan speed. Below 0.35 Mach and above 0.55 Mach, the nozzleexit area is respectively at its maximum and minimum and the fan speedneed not be used to determine the target variable area fan nozzleposition. For air speeds between 0.35 Mach and 0.55 Mach, the fan speedis used to determine a target variable area fan nozzle position.

In FIG. 2, the percent speed value represents the engine operating fanspeed relative to the fan aerodynamic design speed (FEDS). In oneexample, the upper limit is defined at 60% of the FEDS, and the lowerlimit is defined at 75% of the FEDS. In another example, the upper andlower limits are defined respectively 65% and 70% of a particular fanspeed. In the example of 0.45 Mach shown in FIG. 2, if the detected fanspeed is above 70% of a particular fan speed, the target variable areafan nozzle position will be 40% of the maximum open position (point A).If the detected fan speed is less than 65% of a particular fan speed,the target variable area fan nozzle position will be at the maximum openposition (point B in FIG. 2, second position P2 in FIG. 1). For fanspeeds between the lower and upper thresholds 80, 82, the targetvariable area fan nozzle positions are averaged, for example. So, for afan speed of 67% of a particular fan speed, the target variable area fannozzle position is 75% of the maximum open position (point C). In thismanner, the fan speed, or low speed spool rotational speed, is used todetermine the target variable area fan nozzle position at a particularrange of air speed.

The controller 68 can include a processor, memory, and one or more inputand/or output (I/O) device interface(s) that are communicatively coupledvia a local interface. The local interface can include, for example butnot limited to, one or more buses and/or other wired or wirelessconnections. The local interface may have additional elements, which areomitted for simplicity, such as controllers, buffers (caches), drivers,repeaters, and receivers to enable communications. Further, the localinterface may include address, control, and/or data connections toenable appropriate communications among the aforementioned components.

The controller 68 may be a hardware device for executing software,particularly software stored in memory. The controller 68 can be acustom made or commercially available processor, a central processingunit (CPU), an auxiliary processor among several processors associatedwith the computing device, a semiconductor based microprocessor (in theform of a microchip or chip set) or generally any device for executingsoftware instructions.

The memory can include any one or combination of volatile memoryelements (e.g., random access memory (RAM, such as DRAM, SRAM, SDRAM,VRAM, etc.)) and/or nonvolatile memory elements (e.g., ROM, hard drive,tape, CD-ROM, etc.). Moreover, the memory may incorporate electronic,magnetic, optical, and/or other types of storage media. Note that thememory can also have a distributed architecture, where variouscomponents are situated remotely from one another, but can be accessedby the processor.

The software in the memory may include one or more separate programs,each of which includes an ordered listing of executable instructions forimplementing logical functions. A system component embodied as softwaremay also be construed as a source program, executable program (objectcode), script, or any other entity comprising a set of instructions tobe performed. When constructed as a source program, the program istranslated via a compiler, assembler, interpreter, or the like, whichmay or may not be included within the memory.

The Input/Output devices that may be coupled to system I/O Interface(s)may include input devices, for example but not limited to, a keyboard,mouse, scanner, microphone, camera, proximity device, etc. Further, theInput/Output devices may also include output devices, for example butnot limited to, a printer, display, etc. Finally, the Input/Outputdevices may further include devices that communicate both as inputs andoutputs, for instance but not limited to, a modulator/demodulator(modem; for accessing another device, system, or network), a radiofrequency (RF) or other transceiver, a telephonic interface, a bridge, arouter, etc.

The controller 68 can be configured to execute software stored withinthe memory, to communicate data to and from the memory, and to generallycontrol operations of the computing device pursuant to the software.Software in memory, in whole or in part, is read by the processor,perhaps buffered within the processor, and then executed.

Although an example embodiment has been disclosed, a worker of ordinaryskill in this art would recognize that certain modifications would comewithin the scope of the claims. For that reason, the following claimsshould be studied to determine their true scope and content.

What is claimed is:
 1. A method of managing a gas turbine enginecomprising the steps of: detecting an airspeed; detecting a fan speed;referencing a parameter relationship related to a desired variable areafan nozzle position based upon at least airspeed and fan speed, andcomparing the detected airspeed and detected fan speed to the parameterrelationship to determine a target variable area fan nozzle position;and adjusting an actual variable area fan nozzle position in response tothe determination of the target area fan nozzle position and at leastone threshold.
 2. The method according to claim 1, wherein the fan speeddetecting step includes detecting a low speed spool rotational speed,and correcting the fan speed based upon an ambient temperature.
 3. Themethod according to claim 2, wherein the fan speed detecting stepincludes calculating the fan speed based upon a gear reduction ratio. 4.The method according to claim 1, wherein the referencing and comparingsteps include providing a target variable area fan nozzle position for arange of air speeds based upon the fan speed.
 5. The method according toclaim 4, wherein the air speed range is 0.35-0.55 Mach, and the datatable includes first and second thresholds corresponding to lower andupper fan speed limits, the target variable area fan nozzle positionselected based upon the first and second thresholds.
 6. The methodaccording to claim 5, wherein the upper fan speed limit is 60% of anaerodynamic design speed of the fan, and the lower fan speed limit is75% of the aerodynamic design speed of the fan.
 7. The method accordingto claim 5, wherein the upper fan speed limit is 65% of the aerodynamicdesign speed of the fan.
 8. The method according to claim 5, wherein thelower fan speed limit is 75% of the aerodynamic design speed of the fan.9. The method according to claim 1, wherein the adjusting step includesadjusting the target variable fan nozzle position to provide an exitarea of a fan nacelle.
 10. The method according to claim 9, wherein theadjusting step includes translating flaps to selectively block a vent inthe fan nacelle.
 11. The method according to claim 1, wherein the gasturbine engine comprises: a fan arranged in a fan nacelle including aflap configured to be movable between first and second positions; anactuator operatively coupled to the flap; a compressor section fluidlyconnected to the fan, the compressor comprising a high pressurecompressor and a low pressure compressor; a combustor fluidly connectedto the compressor section; a turbine section fluidly connected to thecombustor, the turbine section comprising: a high pressure turbinecoupled to the high pressure compressor via a shaft; and a low pressureturbine.
 12. The method according to claim 11, wherein the gas turbineengine is a geared aircraft engine having a bypass ratio of greater thanabout six (6).
 13. The method according to claim 11, wherein the gasturbine engine includes a low Fan Pressure Ratio of less than about1.45.
 14. The method according to claim 11, wherein the low pressureturbine has a pressure ratio that is greater than about
 5. 15. A gasturbine engine comprising: a fan nacelle including a flap configured tobe movable between first and second positions; an actuator operativelycoupled to the flap; and a controller configured to reference aparameter relationship that relates to a desired variable area fannozzle position based upon at least airspeed and fan speed, thecontroller configured to compare a detected airspeed and a detected fanspeed to the parameter relationship to determine a target variable areafan nozzle position, and the controller configured to provide a commandto the actuator to adjust the flap from a first position to the secondposition in response to the determination of the target variable fannozzle position and at least one threshold.
 16. The gas turbine engineaccording to claim 15, comprising: a fan arranged in the fan nacelle; acompressor section fluidly connected to the fan, the compressorcomprising a high pressure compressor and a low pressure compressor; acombustor fluidly connected to the compressor section; a turbine sectionfluidly connected to the combustor, the turbine section comprising: ahigh pressure turbine coupled to the high pressure compressor via ashaft; and a low pressure turbine.
 17. The gas turbine engine accordingto claim 16, wherein the gas turbine engine is a geared aircraft enginehaving a bypass ratio of greater than about six (6).
 18. The gas turbineengine according to claim 16, wherein the gas turbine engine includes alow Fan Pressure Ratio of less than about 1.45.
 19. The gas turbineengine according to claim 16, wherein the low pressure turbine has apressure ratio that is greater than about
 5. 20. The gas turbine engineaccording to claim 15, wherein the controller is configured to provide atarget variable area fan nozzle position for a range of air speeds basedupon the fan speed, the air speed range is 0.35-0.55 Mach, and the datatable includes first and second thresholds corresponding to lower andupper fan speed limits, the target variable area fan nozzle positionselected based upon the first and second thresholds.